This invention relates to the recording of program materials such as speech or music, and particularly to the recording of program materials which are susceptible to unauthorized duplication or copying using the medium of magnetic tape.
Unauthorized copying or duplication of program material sold by publishers or their licensees is widespread in spite of its illegality and is difficult to police effectively because unauthorized duplicates cannot now be readily distinguished from genuine originals. The result of such copying is to cut seriously into publishers' revenues and to discourage production of expensive, high quality programs. Tape cassettes, in particular, account for most of this activity.
Accordingly, a need exists for techniques and equipment for preparing the original recordings of the program material to leave readily detectable traces or "fingerprints" on the copies which alter upon copying and thus will supply irrefutable proof of the fact that unauthorized copies have been made.
Any technique for preparing original recorded program material to permit detection of magnetic tape duplicates should satisfy several criteria. The technique should be simple to use and accomplished with economical equipment. In addition, the technique should not interfere with normal playback of the material by the possessor of an authorized recording. Moreover, the technique should be one that is difficult for a tape pirate to nullify or sidestep except at an unrewarding cost. Finally, the technique should permit ready and sure identification of a tape recording as an unauthorized copy again without requiring complicated procedures or inordinately expensive equipment.
Heretofore, no techniques or devices have been developed which meet the foregoing criteria satisfactorily.